Single-Cell Technologies for Studying the Evolution and Function of Mitochondrial DNA Heteroplasmy in Cancer

The mitochondrial genome, which encodes genes essential for respiration and cellular homeostasis, is the target of abundant and highly diverse somatic alterations in cancers. Somatic alterations to mitochondrial DNA (mtDNA) nearly always arise heteroplasmically, producing heterogeneous ensembles of mtDNA within single cells. Here, we review new insights derived from exponential increases in genomic sequencing data that have uncovered the nature of, selective pressure for, and functional consequences of cancer-associated mtDNA alterations. As many discoveries have been limited by their ability to determine cell-to-cell variation in mtDNA genotype, we describe a new generation of single-cell sequencing approaches that resolve otherwise indeterminate models of mtDNA heteroplasmy. In tandem with novel approaches for mtDNA editing and modeling of mutations, these advances foreshadow the quantitative dissection of dosage-dependent mtDNA phenotypes that underlie both tumor evolution and heterogeneous response to therapies.